This invention relates to a child-resistant closure for fitment to a container.
The use of child-resistant closures in the packaging of toxic materials, e.g., bleach, liquids containing petroleum distillates, drain cleaners, etc., is well known. Generally, the closures depend upon a releasable, locking relationship between the closure and the container or, for those closures having a base portion attached to the container, between the base portion and an opening and closing cap portion. The most commercially successful closures are those which are designed to stymie the opening efforts of a child, but not frustrate the opening efforts of an adult, especially the elderly, arthritic, etc. A child-resistant closure which is claimed to accomplish such a dual mission is the closure described in U.S. Pat. Ser. No. 4,127,221. This closure features a base portion and a cap portion which is hingedly attached to the base portion. The base portion is fitted to a container and has a top wall with a dispensing orifice. The top wall also carries an upstanding lever member which is flexible and resilient. The lever member has a pawl-shaped end. The cap portion of the closure has a top wall with an opening through which the pawl-shaped end passes when the cap is brought to the closed position. The alignment of the pawl-shaped lever with the cap's top portion is achieved by the configuration of the top of the pawl-shaped lever which acts to distort or bend the pawl-shaped lever and guide it through an opening during the closing cycle. The location of this closing feature (on the pawl-shaped lever) is critical to this closure, allowing the pawl-shaped lever to pass through the cap's top. So passed, the pawl-shaped end achieves a releasable lock between the cap portion and the base portion by overlying that portion of the top wall which is on the edge of the opening. It is critical to the maintenance of the child-resistant feature of this closure that, when the closure is closed, the locations of the opening and the lever member are such that the resilient properties of the lever member will continuously urge the pawl-shaped end against the front edge of the opening, thereby maintaining the overlying position mentioned above. If there is a loss in the lever member's resiliency, the required urging is diminished and the child-resistant feature of this closure could be compromised. Loss in resiliency is not uncommon for a lever member made of a thermoplastic material, especially if the lever member is held under stress over a long period of time. Since many products have a shelf life of months, if not years, the use of this type of closure as a packaging component is not always advisable.
Therefore, it is an object of this invention to provide a closure which has a child-resistant releasable locking system, which system is not adversely affected during the shelf life of a wide variety of products, even if the shelf life is for several years.